The invention relates to an improved fiber opening device for a spinning unit of open-end rotor spinning machines, comprising a fiber opening cylinder in the cavity of an opening housing, said cavity communicating via a cleaning hole with an ejecting duct merging into an impurity withdrawing duct which has, on the one hand, an outlet opening connected to a central impurity withdrawing conduit provided in the machine frame along the spinning units, and, on the other hand, an atmosphere air inlet provided in the front wall of the fibre opening housing; said inlet is adapted to be coupled to a sucking tube of a travelling automatic service unit.
In the German Published Pat. Application (DE-OS) No. 2,555,058 a spinning unit has been described, wherein the front wall of the fiber opening housing is provided with a hole which is in communication with a cleaning space. This hole is adapted to be connected with the sucking tube of the service unit. During cleaning and spinning-in processes, the sucking tube tightly bears on the wall defining the hole of the opening housing. The sucking tube is mounted for reciprocation on said service unit.
However, it has been ascertained by means of practical tests of the aforementioned device that it is not possible to effect the perfect connection between the mouth of the sucking tube and the hole in the front wall of the spinning unit, through which the cleaning duct is in communication with surface of said unit, and that between these elements a gap forms, through which, during the fibre transport, undesirable air is sucked in whereby vacuum losses occur.
With the above-described impurity and fibre withdrawal in view, an eventual leakage is not as serious as with the device disclosed in the Czechoslovak Authorship Certificate No. 240,166, wherein onto the front wall of the spinning unit there is led out only the atmospheric air inlet of the impurity withdrawing duct which merges by its outlet opening into the central conduit on the machine frame, and into which an ejecting conduit opens. The ejecting conduit is connected to the cleaning hole in the cavity of the fiber opening housing. Air continuously flows through the aforedescribed air inlet during the machine operation. During the course of the spinning-in process, the air inlet can be coupled onto the sucking tube whose function is to withdraw initially, spun-in unsuitable fibres at the beginning of the sliver feeding process. Since, however, the withdrawing duct is coupled to the central impurity conduit, and the initial fibres are withdrawn by the sucking tube of the automatic service unit, the vacuum in the sucking tube has to overcome that prevailing in the central impurity withdrawing conduit. In this case, however, any leakage between the sucking tube and the front wall of the fiber opening housing constitutes a considerable shortcoming since it produces problems in the fiber withdrawal. In such a case fibers are taken off imperfectly and accumulate at the transition region between the ejection duct and the withdrawing duct. In extreme cases they may even completely choke these ducts. Simultaneously, the quality of splices and of final yarn is negatively influenced. Another drawback resides in that the sucking effect in the central conduit may cause, in case of a tight connection, the spinning unit to be opened.